Catheter with direct cooling on nonablating element

ABSTRACT

A catheter tip electrode has a tissue contacting surface which electrically conducts RF energy to the tissue and is more thermally conductive than adjacent non-electrically conductive coating or cover which prevents RF conduction to the tissue contacting that surface. The tip electrode has a shell with a nonablating hollow proximal neck portion and a distal ablating portion defining a fluid chamber, and a plug-like support member which is configured with a fluid channel on its outer surface so a fluid passage is provided between the member and the neck portion for convective or direct cooling of the nonablating neck portion and nonconductive tubing covering it.

FIELD OF INVENTION

The present invention relates to catheters that have an active distalportion, including an irrigated tip electrode, particularly useful forablating heart tissue.

BACKGROUND OF INVENTION

Ablation of cardiac tissue is well known as a treatment for cardiacarrhythmias. In radio-frequency (RF) ablation, for example, a catheteris inserted into the heart and brought into contact with tissue at atarget location. RF energy is then applied through electrodes on thecatheter to heat tissue to a destructive temperature in order to createa lesion for the purpose of breaking arrhythmogenic current paths in thetissue.

Irrigated catheters are now commonly used in ablation procedures.Open-loop irrigation provides many benefits including cooling of theelectrode and tissue which prevents overheating of tissue that canotherwise cause adjacent blood to form char and coagulum. Despiteefficient cooling of the electrode tip, under certain circumstances,adjacent catheter tip structures are heated by the tissue lesion siteand the formation of coagulum and/or char can occur on these structureswhich are typically formed from a non-electrically conductive elastomeror plastic. The historic mode of operation relies on a scavenging effectwhere the tip electrode cooling fluid also cools these adjacentstructures to some degree. However, it is desirable for an irrigatedablation catheter to prevent the formation of char and/or coagulum onadjacent, non-ablating tip structures and surfaces by convective anddirect cooling.

Accordingly, it is desirable that an irrigated ablation catheter provideefficient cooling of adjoining non-ablating catheter tip structureswhich, due to their close proximity, are heated by the tissue lesionsite.

SUMMARY OF THE INVENTION

The present invention seeks to minimize, if not prevent, the formationof char and/or coagulum on adjacent structures of an irrigated ablationtip electrode by convectively or directly cooling these structures. Acatheter is constructed with an electrically conductive tip which hasthe benefit of being more thermally conductive than nonconductive orelastomeric structures to which it is bonded. The electrode tip has atissue contacting surface which electrically conducts RF energy to thetissue. The tip has an adjacent surface which is coated or covered witha non-electrically conductive material and such, prevents RF conductionto the tissue contacting that surface. With thermally conductivesubstrate electrode underneath the non-electrically conductive material,the nonablating surface can be cooled by porting to effectively scavengesome of the irrigation flow through the tip electrode to thenon-ablating surface.

Accordingly, the present invention is directed to a catheter having anelongated catheter body and a tip electrode with a shell, an internalsupport member, and an elastomeric tubing wherein the shell has a neckand a chamber, and the support member has a proximal portion inserted inthe neck of the shell and a distal portion extending into the chamber ofthe shell. The proximal portion has a fluid through-hole which is incommunication with a fluid channel provided between the neck of theshell and the proximal portion of the support member to define a fluidpassage between the fluid through-hole and the chamber for cooling theneck of the shell and hence cooling at least a portion of the tubingcovering the neck to minimize formation of char and coagulum thereon. Ina more detailed embodiment, the fluid channel is helical along an outersurface of the proximal portion to maximize surface area exposure of theneck to irrigation fluid for convective cooling.

In another embodiment, the fluid channel has axial and radial branchesto pass fluid to the chamber and to irrigation ports provided in theneck of the shell and a nonconductive tubing of the distal sectioncovering the shell. The irrigation ports allow fluid to pass to theoutside of the tip electrode to directly cool the nonablating areas ofthe tip electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will bebetter understood by reference to the following detailed descriptionwhen considered in conjunction with the accompanying drawings wherein:

FIG. 1 is a perspective view of a catheter in accordance with anembodiment of the present invention.

FIG. 2A is a side cross-sectional view of the catheter of FIG. 1,including a junction between a catheter body and a deflectableintermediate section, taken along a first diameter.

FIG. 2B is a side cross-sectional view of the catheter of FIG. 1,including a junction between a catheter body and a deflectableintermediate section, taken along a second diameter generally orthogonalto the first diameter of FIG. 2A.

FIG. 3 is an end cross-sectional view of the intermediate section ofFIGS. 2A and B, taken along line 3-3.

FIG. 4A is a side cross-sectional view of the catheter of FIG. 1,including a distal section 15, in accordance with an embodiment of thepresent invention.

FIG. 4B is a top plan view of the distal section of FIG. 4A.

FIG. 5 is a perspective view of a shell of a tip electrode, inaccordance with an embodiment of the present invention.

FIG. 6A is a perspective view of a support member of a tip electrode, inaccordance with an embodiment of the present invention.

FIG. 6B is another perspective view of the support member of FIG. 6A.

FIG. 7A is a perspective view of a support member, in accordance withanother embodiment of the present invention.

FIG. 7B is another perspective view of the support member of FIG. 7A.

FIG. 8 is a perspective view of a distal section with the support memberof FIG. 7A, with parts removed for better clarity, in accordance withanother embodiment of the present invention.

FIG. 9 is a perspective view of the distal section of FIG. 8, includinga tip electrode shell with additional irrigated ports in a proximal neckportion.

FIG. 10 is a perspective view of the distal section of FIG. 8, includinga connector tubing with irrigated ports.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates an embodiment of a catheter 10 with an irrigatedablation tip electrode that provides efficient, direct cooling ofadjoining non-ablating catheter tip structures, which due to their closeproximity, are heated by the tissue lesion site. The catheter has anelongated catheter body 12 with proximal and distal ends, anintermediate deflectable section 14 at the distal end of the catheterbody 12, and a distal section 15 with a tip electrode 17 adapted forablation with direct irrigated cooling. The catheter also includes acontrol handle 16 at the proximal end of the catheter body 12 forcontrolling deflection (single or bi-directional) of the intermediatesection 14 relative to the catheter body 12.

With reference to FIGS. 2A and 2B, the catheter body 12 comprises anelongated tubular construction having a single, axial or central lumen18. The catheter body 12 is flexible, i.e., bendable, but substantiallynon-compressible along its length. The catheter body 12 can be of anysuitable construction and made of any suitable material. A presentlypreferred construction comprises an outer wall 20 made of polyurethaneor PEBAX. The outer wall 20 comprises an imbedded braided mesh ofstainless steel or the like to increase torsional stiffness of thecatheter body 12 so that, when the control handle 16 is rotated, theintermediate section 14 of the catheter 10 will rotate in acorresponding manner.

The outer diameter of the catheter body 12 is not critical, but ispreferably no more than about 8 french, more preferably 7 french.Likewise the thickness of the outer wall 20 is not critical, but is thinenough so that the central lumen 18 can accommodate puller members(e.g., puller wires), lead wires, and any other desired wires, cables ortubings. If desired, the inner surface of the outer wall 20 is linedwith a stiffening tube 22 to provide improved torsional stability. Adisclosed embodiment, the catheter has an outer wall 20 with an outerdiameter of from about 0.090 inch to about 0.94 inch and an innerdiameter of from about 0.061 inch to about 0.065 inch.

Distal ends of the stiffening tube 22 and the outer wall 20 are fixedlyattached near the distal end of the catheter body 12 by forming a gluejoint 23 with polyurethane glue or the like. A second glue joint (notshown) is formed between proximal ends of the stiffening tube 20 andouter wall 22 using a slower drying but stronger glue, e.g.,polyurethane.

Components that extend between the control handle 16 and the deflectablesection 14 pass through the central lumen 18 of the catheter body 12.These components include lead wires 30T and 30R for the tip electrode 17and a plurality of ring electrodes 21 carried on the distal section 15,an irrigation tubing 38 for delivering fluid to the tip electrode, acable 33 for an electromagnetic position sensor 34 carried in the distalsection 15, puller wires 32 a, 32 b for deflecting the intermediatesection 14, and a pair of thermocouple wires 41, 42 to sense temperatureat the distal section 15.

Illustrated in FIGS. 2A, 2B and 3 is an embodiment of the intermediatesection 14 which comprises a short section of tubing 19. The tubing alsohas a braided mesh construction but with multiple lumens, for exampleoff-axis lumens 26 a, 26 b, 27, 28. The first lumen 26 a carries apuller wire 32 a for deflection of the intermediate section. Forbi-directional deflection, the diametrically opposing second lumen 26 bcarries a second puller wire 32 b. The third lumen 27 carries the leadwires 30T and 30R, the thermocouple wires 41 and 42, and the sensorcable 33. The fourth lumen 28 carries the irrigation tubing 38

The tubing 19 of the intermediate section 14 is made of a suitablenon-toxic material that is more flexible than the catheter body 12. Asuitable material for the tubing 19 is braided polyurethane, i.e.,polyurethane with an embedded mesh of braided stainless steel or thelike. The size of each lumen is not critical, but is sufficient to housethe respective components extending therethrough.

A means for attaching the catheter body 12 to the intermediate section14 is illustrated in FIGS. 2A and 2B. The proximal end of theintermediate section 14 comprises an outer circumferential notch 25 thatreceives an inner surface of the outer wall 20 of the catheter body 12.The intermediate section 14 and catheter body 12 are attached by glue orthe like.

If desired, a spacer (not shown) can be located within the catheter bodybetween the distal end of the stiffening tube (if provided) and theproximal end of the intermediate section. The spacer provides atransition in flexibility at the junction of the catheter body andintermediate section, which allows this junction to bend smoothlywithout folding or kinking. A catheter having such a spacer is describedin U.S. Pat. No. 5,964,757, the disclosure of which is incorporatedherein by reference.

Each puller wire 32 a and 32 b is preferably coated with Teflon® Thepuller wires can be made of any suitable metal, such as stainless steelor Nitinol and the Teflon coating imparts lubricity to the puller wire.The puller wire preferably has a diameter ranging from about 0.006 toabout 0.010 inch.

As shown in FIG. 2B, portion of each puller wire in the catheter body 12passes through a compression coil 35 in surrounding relation to itspuller wire. Each compression coil 35 extends from the proximal end ofthe catheter body 12 to at or near the proximal end of the intermediatesection 14. The compression coils are made of any suitable metal,preferably stainless steel, and are tightly wound on themselves toprovide flexibility, i.e., bending, but to resist compression. The innerdiameter of the compression coil is preferably slightly larger than thediameter of the puller wire. Within the catheter body 12, the outersurface of the compression coil 35 is also covered by a flexible,non-conductive sheath 39, e.g., made of polyimide tubing. Each portionof the puller wires distal of the compression coil 35 may extend througha respective protective sheath 37 to prevent the puller wire fromcutting into the tubing 19 of the intermediate section 14 duringdeflection.

Proximal ends of the puller wires 32 a and 32 b are anchored in thecontrol handle 16. Distal ends of the puller wires 32 a and 32 b areanchored in the distal section 15, as described further below. Separateand independent longitudinal movements of the puller wires relative tothe catheter body 12, which results in, respectively, deflection of theintermediate section 14 along a plane, are accomplished by suitablemanipulation of a deflection member of the control handle 16.

Suitable deflection members and/or deflection assemblies are describedin co-pending U.S. Publication No. US2010/0168827 A1, published Jul. 1,2010, entitled DEFLECTABLE SHEATH INTRODUCER, and U.S. Publication No.US2008/0255540 A1, published Oct. 16, 2008, entitled STEERING MECHANISMFOR BI-DIRECTIONAL CATHETER, the entire disclosures of both of which arehereby incorporated by reference.

With reference to FIGS. 4A and 4B, at the distal end of the intermediatesection 14 is the distal tip section 15 that includes the tip electrode17 and a relatively short piece of non-conductive connector tubing orcovering 24 between the tip electrode 17 and the intermediate section14. In the illustrated embodiment, the connector tubing 24 has a singlelumen 44 which houses the position sensor 34 and allows passage ofcomponents including electrode lead wires 30T and 30R, the sensor cable33, thermocouple wires 41 and 42, and the irrigation tubing 38 into thedistal section 15 and tip electrode 17. The single lumen 44 of theconnector tubing 24 allows these components to reorient themselves asneeded from their respective lumens in the intermediate section 14toward their location within the distal section 15 and tip electrode 17.In the disclosed embodiment, the tubing 24 is a protective tubing, e.g.,PEEK tubing, having a length ranging between 6 mm and 12 mm, morepreferably about 11 mm.

The tip electrode 17 defines a longitudinal axis 46 and is of at least atwo-piece configuration that includes an electrically conductive domeshell 50 as shown in FIG. 5 and an electrically conductive internalsupport member 52 as shown in FIGS. 6A and 6B, which jointly define acavity or chamber 51 surrounded and enclosed by the shell 50 and thesupport member 52. The shell 50 has a electrically-conductive distalportion 50D adapted for contact with tissue for ablation and anonablating proximal portion 50P. The distal portion 50D has a hollowtubular or cylindrical shape and a closed and rounded atraumatic distalend 53. The proximal portion 50D has a proximal hollow cylindrical neckportion 62 with an open proximal end 54 defined by a rim 55. Formed inshell wall 63 are a plurality of fluid ports 56 that allow fluidcommunication between the cavity 51 and outside the shell.

As shown in FIGS. 4A and 4B, the support member 52 forms a fluid-tightseal at the proximal end 54 of the shell 50. The support member 52 sealsthe interior cavity 51 of the shell 50, and the shell 50 and the supportmember 52 facilitate the provision of a plenum condition within thecavity; that is, where fluid is forced or delivered into it for a moreuniform distribution through fluid ports 56 formed in shell wall 63.

With reference to FIGS. 6A and 6B, the support member 52 has a generallycylindrical body with a distal portion 52D and a proximal portion 52P.At a proximal end of the proximal portion 52P, a radial lip 67 is formedwhich engages with the rim 55 of the shell 50. A proximal surface 55 ofthe proximal portion 52P has a plurality of axial blind holes and axialthrough-holes. In the illustrated embodiment, the proximal surface 55has four blind holes, namely, 57 a, 57 b, 58 and 59, and twothrough-holes 60 and 61 The blind holes 57 a and 57 b are off-axis,diametrically opposed and in longitudinal alignment with the lumens 26 aand 26 b of the intermediate section 14 for receiving and anchoringdistal ends of the puller wires 32 a and 32 b, respectively. The blindhole 58 is off-axis and in general longitudinal alignment with the lumen27 of the intermediate section 14 for receiving and anchoring distalends of the thermocouple wires 41 and 42. The blind hole 59 is off axisand in general longitudinal alignment with the lumen 27 of theintermediate section 14 for receiving and anchoring a distal end of thetip electrode lead wire 30T. The through hole 60 is off-axis andelliptical and in alignment with the lumen 28 of the intermediatesection 14 for receiving and anchoring a distal end of the irrigationtubing 38. The through-hole 61 is on-axis and is in general alignmentwith the lumen of the intermediate section 14 for receiving a distal endof the sensor cable 33.

The through-hole 61 extends through the entire longitudinal length ofthe support member 52, through both the proximal portion 52P and thedistal portion P, thus providing a passage through the support member52. The passage of through-hole 61 has a proximal portion 61P with asmall diameter, a distal portion 61P with a larger diameter forming astep 61S therebetween. The distal portion 62D houses at least a proximalportion of the position sensor 34. A protective tubing 82 may beprovided for a distal portion of the position sensor 34 extending intothe chamber 51. The proximal portion 61P allows the sensor cable 33 toextend proximally from the sensor 34. A proximal end of the sensor 34rests against the step 61S.

The through-hole 60 extends through proximal portion 52P and feeds intoand connects with a fluid channel 65 formed in an outer circumferentialsurface 69 of the distal portion 52D. The channel 65 has a proximalopening 71 and a distal opening 73. In the illustrated embodiment, thechannel 65 is a helical pattern (e.g., about three full loops or 1080degrees) that extends along the length of the distal portion 52D andgives the distal portion an appearance of being “threaded”. The proximalopening 71 communicates with the through-hole 60 and the distal openingcommunicates with the plenum chamber 51. Thus, the channel 65 providesfluid communication between the through-hole 61 and the chamber 51 alongthe outer surface 69 of the distal portion 52D.

With the support member 52 inserted in the shell 50 forming the tipelectrode 17 as shown in FIGS. 4A and 4B, the channel 65 on the outersurface 69 of the distal portion 52D enables significant portions of aninner surface 85 of the neck 62 of the shell 50 lining the channel 65 tobe directly exposed to irrigation fluid delivered by the irrigationtubing 38 to the irrigation through-hole 60. Thus, the neck 62 of theshell 50 is directly cooled by irrigation fluid, which in turn directlycools the connector tubing 24 so as to minimize the formation of charand coagulum on a non-ablating surface of the tip electrode 50.

It is understood that the channel 65 may assume a variety of shapes andpatterns so long as it exposes the inner surface 85 of the shell 50 andits neck 62 to cooling irrigation fluid passed into the tip electrodevia the through-hole 60. Direct cooling of the neck 62 effectively coolsthe connector tubing 24 of the distal section 15 covering the neck 62 ofthe shell 50 and minimizes the formation of char and coagulum on thenonconducting, nonablating surface of the tubing 24.

FIGS. 7A, 7B and 8 illustrate an alternate embodiment of the supportmember 52 a with a dual feeder system with channel 65 having axialbranches and radial branches. Proximal radial branch 92 feeds axialbranch 94 which feeds into the chamber 51. Proximal radial branch 92also feeds axial branch 96 which feeds distal radial branch 98. Distalradial branch 98 is in communication with irrigation ports 90 (FIG. 9)on the neck 62 of the electrode 50P which are aligned and incommunication with irrigation ports 100 (FIG. 10) in the tubing 24. Theports 100 allow irrigation fluid to pass to the outside for directlycooling the nonconductive, nonablating neck 62.

The total hydraulic resistance (combined resistance of the ports as wellas the branches) should be balanced between the branches that feed theneck 62 and those that feed the chamber 51 such that both zones of thetip are irrigated. This can be accomplished by varying the number andsize of the fluid ports 56 of the shell 50. In one embodiment, the ports56 have a diameter of about 0.0035 in. Additionally, the cross sectionalarea of the branches can be adjusted to increase or reduce the hydraulicresistance of any given branch. FIG. 7B shows the branch 94 feeding thechamber 51 having a “flat” surface 102 on the outer surface of thedistal portion 52D of the support member 52. Varying the depth of theflat surface will inversely change the effective cross section of thebranch 94. In a similar manner, the T shaped intersection of branches92/96 and 96/98 can be varied in both width and depth to affect itshydraulic resistance. Varying the geometry of the feeder branchesthemselves provides an additional parameter for tuning the flowdistribution between the neck and plenum zones beyond adjustment of theport sizes and numbers alone. As discussed in patent application Ser.No. 12/769,592 Clark et al, it is helpful to consider the DiffusionRatio which is the sum total of the output area (irrigation ports)divided by the input area (fluid lumen cross section). In the case ofthe electrode with both conductive and non-conductive irrigatedsurfaces, it will be helpful to either reduce the number and size ofirrigation ports or increase the diameter of the fluid lumen in order topreserve the overall diffusion ratio at approximately 2 or less, andmore ideally at 1.3 or less.

The shell 50 and the support member 52 are constructed of abiocompatible metal, including a biocompatible metal alloy. A suitablebiocompatible metal alloy includes an alloy selected from stainlesssteel alloys, noble metal alloys and/or combinations thereof. In oneembodiment, the shell is constructed of an alloy comprising about 80%palladium and about 20% platinum by weight. In an alternate embodiment,the shell 50 and the member 52 are constructed of an alloy comprisingabout 90% platinum and about 10% iridium by weight. The shell can formedby deep-drawing manufacturing process which produces a sufficiently thinbut sturdy shell wall that is suitable for handling, transport throughthe patient's body, and tissue contact during mapping and ablationprocedures.

As shown in FIG. 4A, distal ends of the thermocouple wires 41 and 42 maybe covered in a nonconductive cover or sheath 75, for example, apolyester heat shrink sleeve. The sheath 75 is an electricallyinsulating, second protective covering over the thermocouple wires(proximal to thermocouple junction 80) to prevent abrasion against thesupport member 52. Surrounding a distal portion of the sheath 75 may beanother nonconductive tubing 76, for example, a polyimide tubing. Thetubing 76 is constructed of a thermally conductive material whichprovides electrical isolation between the thermocouple junction 80 andthe support member 52 which is energized with RF potential.

In the illustrated embodiment, the sensor 34 and cable 33 arefront-loaded into the support member 52 during assembly of the tipelectrode 17. That is, before the shell 50 is mounted on the supportmember 52, the sensor 34 and its cable 33 are fed (proximal end of thecable first) into the through hole 61 from the distal end of the supportmember. A distal end of the tubing 82 covering the sensor 34 is filledand packed with a suitable adhesive so as to seal the tubing 82 againstfluid leakage from the cavity 51. The shell 50 is then mounted on thesupport member 52 with the distal portion 52 extending into the cavity51, the proximal portion 52D filling the neck 62 and the rim 55 abuttingagainst the lip 67. The rim and the lip are soldered to fixedly attachthe shell 60 and the support member 52.

As shown in FIGS. 4A and 4B, ring electrodes 21 may be mounted on theconnector tubing 24 of the distal section 15. They may be made of anysuitable solid conductive material, such as platinum or gold, preferablya combination of platinum and iridium. The ring electrodes can bemounted onto the connector tubing 24 with glue or the like.Alternatively, the ring electrodes can be formed by coating the tubing24 with an electrically conducting material, like platinum, gold and/oriridium. The coating can be applied using sputtering, ion beamdeposition or an equivalent technique. The number of the ring electrodeson the tubing 24 can vary as desired. The rings may be monopolar orbi-polar. In the illustrated embodiment, there is a distal monopolarring electrode and a proximal pair of bi-polar ring electrodes. Eachring electrode is connected to a respective lead wire 30R.

As understood by one of ordinary skill in the art, each lead wire 30R isattached to its corresponding ring electrode by any suitable method. Apreferred method for attaching a lead wire to a ring electrode involvesfirst making a small hole through the wall of the tubing 24. Such a holecan be created, for example, by inserting a needle through thenon-conductive covering and heating the needle sufficiently to form apermanent hole. The lead wire is then drawn through the hole by using amicrohook or the like. The end of the lead wire is then stripped of anycoating and welded to the underside of the ring electrode, which is thenslid into position over the hole and fixed in place with polyurethaneglue or the like. Alternatively, each ring electrode is formed bywrapping a lead wire 30R around the non-conductive tubing 24 a number oftimes and stripping the lead wire of its own insulated coating on itsoutwardly facing surfaces.

The tip electrode 17 is electrically connected to a source of ablationenergy (not shown) by the lead wire 30T. The ring electrodes 21 areelectrically connected to an appropriate mapping or monitoring system byrespective lead wires 30R.

The lead wires 30T and 30R pass through the lumen 27 (FIG. 3) of thetubing 19 of the deflectable intermediate section 14 and the centrallumen 18 of the catheter body 12. The portion of the lead wiresextending through the central lumen 18 of the catheter body 12, andproximal end of the lumen 27 can be enclosed within a protective sheath(not shown), which can be made of any suitable material, preferablypolyimide. The protective sheath is anchored at its distal end to theproximal end of the intermediate section 14 by gluing it in the lumen 27with polyurethane glue or the like. Each electrode lead wire has itsproximal end terminating in a connector at the proximal end of thecontrol handle 16.

The preceding description has been presented with reference to certainexemplary embodiments of the invention. Workers skilled in the art andtechnology to which this invention pertains will appreciate thatalterations and changes to the described structure may be practicedwithout meaningfully departing from the principal, spirit and scope ofthis invention. It is understood that the drawings are not necessarilyto scale. Accordingly, the foregoing description should not be read aspertaining only to the precise structures described and illustrated inthe accompanying drawings. Rather, it should be read as consistent withand as support for the following claims which are to have their fullestand fairest scope.

What is claimed is:
 1. A catheter, comprising: an elongated catheterbody; a tip electrode distal to the catheter body; the tip electrodecomprising: a shell having a proximal neck portion and a distal chamber;a support member having a proximal portion and a distal portion, theproximal portion inserted in the neck portion of the shell and thedistal portion extending into the chamber of the shell, the proximalportion having a fluid through-hole; and a fluid channel providedbetween the neck portion of the shell and the proximal portion of thesupport member to define a fluid passage between the fluid through-holeand the chamber.
 2. The catheter of claim 1, further comprising aposition sensor at least partially housed in the distal portion of thesupport member.
 3. The catheter of claim 1, wherein the fluid channel isformed on an outer surface of the distal portion of the support member.4. The catheter of claim 3, wherein the fluid channel has a helicalpattern on the outer surface.
 5. The catheter of claim 3, wherein thefluid channel has axial and radial branches.
 6. The catheter of claim 4,wherein the helical pattern extends at least about 360 degrees along alength of the distal portion of the support member.
 7. The catheter ofclaim 4, wherein the helical pattern extends at least about 720 degreesalong a length of the distal portion of the support member.
 8. Thecatheter of claim 4, wherein the helical pattern extends at least about1080 degrees along a length of the distal portion of the support member.9. The catheter of claim 1, wherein the proximal portion of the supportmember includes a through-hole and the channel has a proximal opening incommunication with the through-hole and a distal opening incommunication with the chamber.
 10. The catheter of claim 1 wherein theshell has a shell wall formed with fluid ports to allow fluid inside thechamber to flow to outside the chamber.
 11. A catheter, comprising: anelongated catheter body; a tip electrode distal to the catheter body;the tip electrode comprising: a shell having a distal chamber and aproximal neck portion; and a support member having a proximal portionand a distal portion, the proximal portion inserted in the neck portionand the distal portion extending into the chamber, the proximal portionhaving a fluid through-hole, the distal portion having an outer surfacefacing an inner surface of the neck portion of the shell and a channelformed on the outer surface that provides a fluid passage between thefluid through-hole and the chamber, wherein the inner surface of theneck portion is adapted for exposure to fluid passing through the fluidpassage.
 12. The catheter of claim 11, further comprising a positionsensor at least partially housed in the distal portion of the supportmember.
 13. The catheter of claim 11, wherein the fluid channel has ahelical pattern on the outer surface.
 14. The catheter of claim 11,wherein the fluid channel has axial and radial branches.
 15. Thecatheter of claim 13, wherein the helical pattern extends at least about360 degrees along a length of the distal portion of the support member.16. The catheter of claim 13, wherein the helical pattern extends atleast about 720 degrees along a length of the distal portion of thesupport member.
 17. The catheter of claim 13, wherein the helicalpattern extends at least about 1080 degrees along a length of the distalportion of the support member.
 18. The catheter of claim 11, wherein theproximal portion of the support member includes a through-hole and thechannel has a proximal opening in communication with the through-holeand a distal opening in communication with the chamber.
 19. The catheterof claim 11, wherein the catheter also has a connector tubing, a distalportion of which covers the neck portion, the neck portion and thedistal portion of the connector tubing having aligned irrigation portsconfigured to allow irrigation fluid to pass from the channel to outsidethe tip electrode to cool an outer surface of the connector tubing.